The present invention relates to apparatus useful to exchange and generate heat and moisture in respiratory gas applications. More particularly, the invention relates to apparatus for heating and humidifying respiratory gases which exchange heat and moisture with respiratory gases and generate heat and moisture available to heat and humidify respiratory gases.
During surgery and other medical procedures, a patient is frequently connected to an anesthesia machine or ventilator to provide respiratory gases to the patient. The respiratory gases passed to the patient are advantageously heated and humidified so that the gases entering the patient are of a suitable temperature and humidity so as not to adversely impact the patient. Heat and moisture exchangers (HMEs) are often used to provide heat and humidity to the respiratory gases entering the patient. Typically, these HMEs are located so that respiratory gases from the patient pass through a tracheal tube into the HME, which is often a fibrous or other gas permeable material, which accumulates or collects heat and moisture from the exhaled gases. During the inhaling of respiratory gases, for example, from an anesthesia machine, the HME provides both heat and moisture to these respiratory gases prior to the gases entering the patient. Over a period of time, the HME is effective to maintain a certain level of temperature and humidity in the respiratory gases entering the patient.
Such HMEs do, however, have certain drawbacks. For example, during the initial or start up phase of the operation of a HME member, the amount of heat and moisture being exchanged out of the HME member to the respiratory gases being passed back to the patient is relatively low, for example, because the HME member is at a reduced temperature and a reduced moisture content. This "start up" problem can adversely affect the patient. One approach to overcoming at least a portion of this problem is to provide the HME member with a hygroscopic component, for example, calcium chloride and the like components, which is effective to generate a limited amount of heat as the exhaled gases leaving the patient pass through the HME member. This provides a "quick warm up" HME member and at least provides a heated respiratory gas stream to the patient relatively quickly. However, the degree of humidification of the respiratory gases being passed to the patient still is relatively low during the first portion of the HME member operation, in part because of the water held by the hygroscopic component.
In addition, the inefficiencies of the typical HME member are such that a certain portion of the heat and moisture collected by the HME is lost, for example, to the environment and otherwise, rather than being passed back to the patient by exchange with respiratory gases. The degree of heating and/or humidification of the respiratory gases varies, and in particular decreases, over time which can adversely impact the patient.
It would be advantageous to provide a system by which respiratory gases can be effectively, reliably, straightforwardly and controllably provided with both heat and moisture so that the comfort and safety of a patient undergoing surgery and/or other medical treatment is enhanced.